As an improvement over the spray painting of articles such as automobile bodies and household appliances, a new kind of sheet material has been developed to provide protective and decorative coatings. The new material comprises a thin, flexible, stretchable, thermoplastic support sheet, known as a carrier film, which has a protective and decorative paint layer on one side and an adhesive on the other side. Optionally, it can also have other layers such as a tie or bonding layer between the paint and the carrier film and a clearcoat over the paint or basecoat layer. Using the known procedure of thermoforming, the sheet material can be stretched and bonded to an article such as an automobile body panel. Important advantages over spray painting include economy in the use of paint and avoidance of air pollution by evaporating solvents. Furthermore, the new material has a remarkably more attractive appearance than spray painted finishes.
The new type of sheet material and a process for its manufacture are described in the U.S. Patent Application of G. G. Reafler, Serial No. 116,426, filed Nov. 3, 1987. The process involves providing a laminar flow of the coating composition on the surface of the thermoplastic carrier film to form a layer of substantially uniform thickness, followed by a drying procedure, then coating and drying each additional layer in sequence to obtain a finished product of excellent gloss and smoothness.
The present invention provides a further improvement in the form of a new drying procedure for the paint layer of such sheet material. Although the layers of the sheet material of the Reafler patent application can be dried by conventional procedures, it has been found that because of its complex composition and its thickness, the paint layer is particularly sensitive to the drying conditions.
The paint layer is formed from a latex paint composition comprising a colloidal suspension in water of water-insoluble elastomeric polymers and also contains one or more higher boiling organic solvents which function as coalescing agents or have other purposes. A composition of this kind, when dried on the stretchable thermoplastic support film, has the flexibility, stretchability and durability that are necessary for sheet material that is to be stretched and adhered to automobile panels and the like. Such a paint composition dries reasonably well when applied by spray painting in thin layers directly to automotive body panels, since much of the liquid evaporates when sprayed. In this respect spray painting differs markedly from laminar flow coating in which little or no liquid evaporates as the composition is coated on the carrier film support. In any event, the drying defects that occur when a spray painted layer is dried in a conventional drying oven apparently do not noticeably worsen the otherwise lower quality of spray painted finishes.
With the new sheet material for applying finishes to automobile body panels, a new level of quality is the rule. Defects such as small blisters and "solvent pops" are no longer considered acceptable. This has led to the need for an improvement in the procedure for drying the paint layer so that wide sheet material can be produced with minimal loss of product as waste caused by bubble defects which originate in the paint layer. In accordance with the present invention a new method is provided which is particularly adapted for drying a thick paint layer coated on a heat-deformable plastic film when the wet paint layer contains a coalescable and hardenable, film-forming polymer colloidally dispersed in water with one or more higher boiling organic solvents.